The aim of the DCAN (Devolved Control ATM Networks) project is to
design and develop the necessary infrastructure for scalable control
and management of multiservice Networks.

DCAN starts from the premise that control/management functions of
the various devices that make up such a network - typically ATM
switches - should be extracted from the devices themselves and be
delegated to external workstations dedicated to that purpose.

By devolving the management and control of switches and end devices
into a coherent external system, one escapes the need for switch and
device manufacturers to capture these functions within their
equipment. This enables customers to configure their systems in a
manner best suited to their needs. In addition, it enables new
management and control policies to be introduced in the network
without modifying every switch, and thus will allow legacy and new
signalling and management systems to co-exist.

DCAN also presumes that the control/management of Multi-Service
networks is necessarily distributed due to, amongst other reasons, the
need for end-to-end resource allocation in order to give guarantees
about Quality of Service (QoS).

Finally DCAN takes into the account the fact that extracting
control functions from the networks device and placing them into
workstations requires us to be able to place real-time constraints on
the execution of the software performing those control functions.

Thus to be successful, DCAN must address both real-time OS and
Distributed Processing Environment issues.

It is intended that the designed and implemented infra-structure be
scalable. Scalable here does not just refer to size; rather it means
being able to cope with a range of system capabilities, including
simple devices with limited functionality. Thus, while retaining
compatibility with developments in telecommunication system
management, the emphasis is on ATM networks used to interconnect
workstations and simple devices.

In what follows we distinguish from the two related areas of
management and control. Control:

is performed on a short time scale, management operation may
takes minutes or even hours to perform;

does not require the intervention of a human operator,
management in general does;

is management policy independent, i.e. control functions are
carried out regardless of what management strategy is being used.

For example, call set-up is a typical control function and alarm
correlation a management function. Although, control and management to
some extent overlap and are often referred together simply as network
management it is still useful to make a distinction between them.

Current developments in ATM Networking are leading to the notion of
devolved control in which a number of switches are controlled by a
largely separate distributed system as shown below:

This approach is in line with current thinking in Intelligent
Networking (IN), whereby typically the actual routing of a call is
achieved outside of the network by some higher level entity which then
uses knowlege about the type of call being made in order to determine
what script to run in order to perform the service e.g. freephones
charge the callee rather than the caller.

In addition, it resonates with the approach to telecommunication
management as specified by the ITU-TS Reference Model for Open
Distributed Processing (X.901-4), which defines a Telecommunication
Management Network (TMN) which manages the underlying
telecommunication network.

However, both IN and TMN standards have been defined with a Public
Switching Telecommunication Network in mind. Within such a wide-area
environment one may assume that network elements are autonomous and
powerful; neither processing power nor implementation complexity are
primary limitations.

In local ATM networks, this assumption may not hold. Switches may
only perform the relaying of cells (unicast or multicast) with even
simple connection and network management functions performed by an
external (distributed) system. There may also be end system elements,
such as an ATM camera, which are so simple that they cannot perform
network signalling and thus may not be able to initiate communication.
They can be thought of as slaves.

Furthermore, the IN and TMN standards have defined complex
protocols between the managing and managed layers. The rational seems
to be that all embracing protocols will enhance their adapability to
new services. For managed elements to be able to communicate with a
manager using such protocols require them to have some knowledge of
the management strategy.

We take the view that the protocols between the manager and the
network should be minimalist. Additional management functionality e.g.
synchronisation between streams, can be added in the management
domain.

We propose to develop a system which allows the distributed
management platform to encompass a range of intelligences and to make
as few assumptions as possible about the management strategy to be
used.

The work divides naturally into four related, but distinct domains:

development of a suitable platform in which to run management
and control applications and some test control/ management
applications in order to demonstrate the concept;

development of a suitable means of communication between these
applications;

development of a suitable simple protocol for the communication
of management and control information between the network devices
and these applications;

construction of a network consisting of devices - ATM
peripherals and switches - capable of being managed by the above.

The consortium is composed of APM Limited, Nemesys Research Limited and
the University of Cambridge Computer Laboratory.

APM Limited,
whose origins can be traced to the ANSA Alvey project begun in 1984,
is a pioneer in the field of distributed computing. It has developed
the ANSA architecture for distributed systems and ANSAware, an
implementation of the architecture which runs on a number of vendor
operating systems. It was founded as a limited company in 1989.

Fore Audio Video
Systems Ltd (formerly Nemesys Research), is an ATM end system
manufacturer, specialising in products that can take multiple audio
and video feeds and send them over an AT M network.

The University of CambridgeComputer Laboratory has a great
deal of experience in distributed computing and ATM networks. It
developed the original IPR which led to the AVA-200 which was
exploited by Nemesys Research.